Field of the Invention
The present invention relates to a method and to a magnetic resonance apparatus for acquiring MR data from a slice of a volume segment within an examination subject, in particular in the presence of magnetic field inhomogeneities.
Description of the Prior Art
In order to suppress metal artifacts in SE (Spin Echo)-based sequences (such as TSE (Turbo Spin Echo), for example), a SEMAC method can be used, see “SEMAC: Slice Encoding for Metal Artifact Correction in MRI”, W. Lu et al., Magnetic Resonance In Medicine 62, pp. 66-76, 2009. This involves carrying out an additional coding in the direction of the slice while using a conventional two-dimensional protocol or slice-based scan. This coding corresponds to a phase coding and is also known as “SEMAC-encoding”. With this method, the scanning time increases linearly with the number of additional phase coding steps in the slice selection direction, which are also referred to as SEMAC steps. In particular with T2-weighted TSE-protocols with a long repetition time TR, the entire scanning time clearly increases.
For example, to acquire a slice with 256 phase coding steps in a TSE-sequence with a turbofactor of 8 and a repetition time TR of 4 seconds, a scanning time of 2 minutes and 8 seconds is required. If eight SEMAC steps are used to suppress metal artifacts, the scanning time increases to over 17 minutes, which is clearly too long for clinical protocols.